Method of manufacturing closed end tubular products



6, 1969 A. E. WESTIN 3,462,987 I METHOD OF MANUFACTURING CLOSED END TUBULAR PRODUCTS Filed May 15, 1967 2 Sheets-Sheet 1 INVENTOR flxa M45527 Aug. 26, 1969 A. E. WESTIN 3,462,987

METHOD OF MANUFACTURING CLOSED END TUBULAR PRODUCTS Filed May 15, 1967 2 Sheets-Sheet 2 STATION 1 I M. I 1.. H I m...

STATION 2 I INVENTOR 41H. 5 war/1v Jf/argre 5 United States Patent 3,462,987 METHOD OF MANUFACTURING CLOSED END TUBULAR PRODUCTS Axel E. Westin, Milwaukee, Wis., assignor of thirty percent to Elwin A. Andrus, Milwaukee, Wis. Filed May 15, 1967, Ser. No. 638,424 Int. Cl. B21b 19/04 US. CI. 72-97 3 Claims ABSTRACT OF THE DISCLOSURE The piercing of a heated billet to a point short of the trailing end to leave the end closed and free from the usual incipient piercing crack or rupture, by initially reducing the diameter of the trailing end so that the rolls lose their traction upon the blank prior to reaching the end, and a zone of gradual reduction in roll pressure is provided that substantially eliminates the crack or rupture by the time the piercing operation terminates.

This invention relates to a method of manufacturing closed end tubular products such as gas bottles, cylinders, bomb casings and the like.

Heretofore, methods employed that started with the piercing of a hot billet to form the tubular shell as in conventional roll-type piercing mills required that the entire length of the billet be pierced and that one end of the resulting tubular blank be thereafter formed and closed by forging or spinning processes.

It has been thought impossible to stop the piercing operation short of the far end of the billet, because an incipient crack or rupture precedes the tip of the piercing mandrel often for as much as one and a half inches as the billet progresses over the mandrel. Any attempt to stop short of the end of the billet results in a problem of how to eliminate the rupture referred to and which prevents the forming of a desired end closure free from defects.

The present invention provides a method which permits the piercing of a billet short of the far end Without leaving the defect of an incipient rupture in the metal remaining at the closed end of the billet.

In carrying out the invention in its broadest sense the roll pressure is gradually relieved as the trailing end of the billet approaches the piercing zone, thereby reducing the traction until the piercing operation practically ceases.

As a practice method for carrying out the invention, the far end of the billet is initially prepared by tapering it, preferably in a die pressing operation after it comes from the furnace and before starting the piercing operation, to reduce the diameter of the billet for a distance from the end.

The purpose of this tapering operation is to relieve the pressure of the piercing rolls upon the billet as it moves through the rolls and reaches the point where it is desirable to stop the piercing action. The rolls cease to drive the billet over the piercing plug or mandrel at this point by reason of the release of pressure contact with the billet.

Thus, the piercing operation proceeds normally until it approaches the far end of the billet and the gradual release of pressure contact of the rolls upon the billet as the latter approaches the point where piercing ceases results in a gradual elimination of the rupture that normally advances ahead of the piercing mandrel. In this regard the invention is based upon the realization that the high pressure of the rolls upon the billet in relation to the piercing mandrel causes the rupture, and as that pressure gradually decreases until piercing ceases the rupture is gradually reduced to a point of elimination.

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The method of the invention is illustrated in the accompanying drawings in which:

FIGURE 1 is a schematic illustration of a piercing operation with the billet sectioned;

FIG. 2 is a schematic illustration of the termination of the piercing operation as the rolls register with the portion of reduced diameter near the end of the billet; and

FIG. 3 is a flow chart of the method in its basic steps, it being understood that additional intermediate steps may be needed depending upon the final dimensions required.

Referring to the drawing, and particularly to FIG. 3, the billet is first heated in furnace 1 and then goes to the preliminary end reducing operation at station 2; after which the billet enters the piercing mill 3. When the billet reaches the position illustrated in FIG. 2 where the reduced end terminates the driving contact of the rolls, the mandrel is retracted, moving the billet on through the mill to clear the rolls, and the piercing mandrel is removed from the blank to strip the latter from the plug or mandel, after which the blank goes to station 4 where a die mandrel enters it and forms the closed end in a suitable die.

Starting from the beginning in more detail the billet 5 as it comes from the furnace 1 is given a nosing operation at the trailing end as shown in FIG. 3 to reduce the diameter of the billet in a zone 6 so that the rolls of the piercing mill 3 will not grip the blank in the region of the trailing end. The slight nosing operation is preferably accomplished by a hydraulic press 7 which forces the billet longitudinally into a tapered die recess 8 and at the same time forms a central recess 9 in the opposite end for centering the billet on the piercing plug or mandrel 10. The transition in diameter of the billet in zone 6 is preferably gradual for a sufiicient distance to eliminate formation of the undesirable crack or rupture 11 ahead of the piercing plug 10.

FIG. 1 shows the formation of the rupture 11 ahead of the piercing plug 10 as the billet is forced over the plug by the rolls 12 in the direction of the arrow.

When the rolls reach the zone 6 shown in FIG. 2, the gradual reduction in pressure contact of the rolls gradually shortens and ultimately eliminates the crack or rupture formation as the rolls gradually cease to drive the billet forward over the plug 10. This leaves the billet with a reasonably thick closed end free from rupture.

The partially pierced billet, now blank 13 and the plug 10 are then moved together in the direction of former billet movement until the blank 13 clears the rolls 12 and the piercing plug continues until it is fully withdrawn from the blank, and the latter thus stripped from the plug.

The blank 13 then moves to station 4 where a die mandrel 14 enters the blank, pushes it through the die 15 to reduce the wall thickness and then presses the closed end into a suitable forming die 16 to give at least a preliminary shaping of the end closure for the final product 17. If additional forming is required to arrive at the desired final shape and dimensions any number of additional forging operations may be applied. Likewise, where it is desired to reduce the wall thickness or to size the blank, these operations can be added utilizing conventional methods and apparatus. Normally reheating will not be necessary, but where needed it may be provided.

In carrying out the invention the zone 6 of gradual reduction in diameter of the billet should be sufficiently long to eliminate the crack or rupture 11 as the rolls reach the point of insufiicient traction on the billet to continue the piercing operation. Further extension of zone 6 beyond this point is of no advantage, except that the remaining zone 6 to the end of the billet should be of reduced diameter so that the blank 13 may be drawn freely out of the rolls with the mandrel as previously explained. It is possible to keep a light traction for the rolls to the very end of the billet, thereby permitting the rolls to push the blank on through during initial release and withdrawing of the plug or mandrel.

Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

I claim:

1. The piercing of a heated billet in the production of a closed end tubular product in a roll-type piercing mill, in which the pressure of the rolls upon the billet is gradually reduced near the trailing end of the billet until the piercing operation substantially stops, leaving a closed end of the billet substantially free of an internal incipent crack.

2. The piercing of a heated billet in the production of a closed end tubular product in a roll-type piercing mill having a piercing plug and rolls operated therewith, in which the trailing end of the billet is initially tapered to a reduced diameter to provide a zone of progressive reduction in roll pressure upon the billet and a stopping of the piercing operation ahead of the end of the billet at a position where the central incipient crack ahead of the piercing plug is substantially eliminated.

3. The method of claim 2 in which the reduction in diameter of the trailing end of the billet is insufiicient to eliminate all traction between the rolls and the billet, and upon stopping of the piercing operation the piercing plug or mandrel is released to permit movement thereof with the billet until the latter is clear of the rolls, and thereafter the billet is stripped from the piercing plug or mandrel.

References Cited UNITED STATES PATENTS 750,824 2/1904 Davis 72-97 CHARLES W. LANHAM, Primary Examiner L. A. LARSON, Assistant Examiner 

